This article is a commentary on a study published in The Lancet, 2002; 360:1646-52. The article by Hedley AJ. presents one of the studies conducted following the implementation of sulfur restrictions in fuel oil in Hong Kong. The observed results, in terms of health benefits, appear modest compared to other studies, but this may be an incomplete estimate due to the type of analysis (time series) that considers only short-term effects. A prospective cohort follow-up study would seem better suited to quantify the total impact of the measure implemented. However, while numerous studies had demonstrated that increases in pollution could lead to an increase in mortality affecting primarily vulnerable individuals—though without being able to precisely estimate by how much time these deaths had been “precipitated”—this approach made it possible to quantify the gain in life expectancy for individuals exposed to reduced sulfur pollution. The authors compare this study with other similar research conducted primarily in Europe, some of which did not demonstrate a clear causal link between SO2 levels and mortality. However, they emphasize that concentrations of respirable particulate matter (whose health effects are well documented), even though they did not show variation before and after the event, are significantly higher in Hong Kong. Consequently, combined and synergistic effects of SO2 and other pollutants cannot be ruled out. (Conclusion).